Light emitting diodes (LEDs) convert electrical energy into optical energy. In semiconductor LEDs, light is usually generated through recombination of electrons and holes within a semiconductor layer. A challenge in the field of LEDs is to extract as much of the emitted light as possible toward the desired direction. Various approaches may be used to increase the efficiency of an LED, such as adjusting the shape of the semiconductor layer, roughening the surface of the semiconductor layer, and using additional optics to redirect or focus the light.
Micro-LEDs are being developed for various applications in display technology. A micro-LED has a very small chip size. For example, a linear dimension of the chip may be less than 50 μm or less than 10 μm. The linear dimension may be as small as 2 μm or 4 μm. However, micro-LEDs typically have a lower efficiency than large-power LEDs. While large-power LEDs may have a light extraction efficiency (LEE) of up to 90%, micro-LEDs typically have a LEE on the order of 10% within an emission cone having an angle of 90°, and 0.5% within an emission cone having an angle of 10°. For example, a large-power LED or a micro-LED, such as the planar LED 800 shown in FIG. 29, typically has a planar LED Lambertian pattern 830 with a full-width at half-maximum (FWHM) of approximately 120° and a half-width at half-maximum (HWHM) of approximately 60°. A vertical micro-LED, similar to the hemispherical LED 810 shown in FIG. 29, typically has a hemispherical LED pattern 840 with a HWHM greater than or equal to 60°, in which side wall emission may lead to bunny ears. Further, a parabolic LED 820 typically has a parabolic LED emission 850 with a more narrow profile having a HWHM less than 60°, and typically between 20° and 40°. Accordingly, it would be advantageous to increase the LEE of micro-LEDs, and to provide an output beam with a narrower beam profile.